[mytherin]

You are misinterpreting it indeed.

The scenario I am describing is roughly the following:

Suppose we allocate 100K buffers that all have an equal size, and our memory usage is now 10GB. After that point we free 20K buffers, but allocate 10K more. In other words, from that point on we are freeing more buffers than we are allocating.

Now, since we are freeing more than we are allocating, you would expect our memory usage to go down. However, when using the standard glibc malloc on Linux, our memory usage unexpectedly goes up. After this happens several times in a row the system runs out of memory and new calls to malloc fails.